hi this is Peter from Anatomy Zone and in this tutorial we're going to go through the anatomy of the eyeball this video is a collaboration between Anatomy Zone and teachmeanatomy doino check out the links in the video description below for some useful articles to accompany this video tutorial the eyeball is a bilateral and spherical organ which houses the structures responsible for vision it lies in a bony cavity within the facial skeleton known as the Bony orbit take a look at my previous tutorial to learn about the anatomical features of the Bony orbit anatomically the eyeball can be divided into three parts the fibrous vascular and inner layers these layers have different structures and functions let's start with the outermost layer the fibrous layer I've switched over now to a view of the isolated eyeball with some layers dissected away the layer of the eye is the outermost layer it consists of the Scara and the cornea which are directly continuous with each other you can see the shape and continuity of the cornea with the Scara from this lateral view their main functions are to provide shape to the eye and support the deeper structures the Scara comprises the majority of the fibrous layer approximately 85% and provides a attachment to the extraocular muscles the extraocular muscles are responsible for the movement of the eye check out my previous tutorial for more information on these muscles in addition several vessels and nerves penetrate through the Scara including the optic nerve which you can see here posteriorly the Scara is visible as the white part of the eye the cornea is continuous anteriorly with the Scara and is transparent and positioned centrally at the front of the eye light entering the eye is refracted by the cornea the vascular layer of the eye lies underneath the fibrous layer it consists of three continuous Parts the choid the cery body and the iris the choid is a layer of connective tissue and blood vessels it provides nourishment to the outer layers of the retina I've switched over to an anterior view showing the whole eyeball to show you the cery body which I've highlighted in green you can see how it encircles the eyeball the cery body itself is comprised of two parts the celery muscle and cery processes I've sliced the eyeball in half and we've rotated around to look at the eyeball in section let's just review the structures that we have already discussed so that you are oriented to this view you can see the the outer fibrous Scara in continuity with the corer anteriorly you can also see the inner vascular choid and the CER body here in green the cery muscle consists of a collection of smooth muscle fibers arranged in three orientations longitudinal circular and Radial when these muscles contract the diameter of the circular cery body reduces in size projecting from the surface of the cery body are the cery processes these attach the lens to the cery body via these fibers which you can see here known as zonular fibers collectively the zonular fibers form the suspensory ligament of the lens the cery body therefore controls the shape of the lens as I mentioned before when the cery muscle contracts the circular CER body reduces in size when this happens the zonular fibers therefore slacken reducing the tension applied to the outside of the lens allowing the lens to return to a more rounded shape this process is known as accommodation and adjusts the lens for near Vision conversely when the cery body is relaxed the diameter of the cery body is greater which means the zonular fibers are held tight pulling the lens flat this optimizes the lens for long distance Vision in addition to a adjusting the lens shape the cery body also contributes to the formation of aquous humor the final structure of the vascular layer is the iris this is a circular structure with an aperture in the center called the pupil the iris is the component of the eye which gives you your eye color it has two Arrangements of fibers which control the size of the pupil circular fibers and radi fibers the circular fibers make up the sphincter pupilli muscle which is innovated by the parasympathetic nervous system activation of this system causes constriction of the pupil which thereby limits the amount of light that can enter the eye the radial fibers on the other hand make up the dilator pupil muscle which are innovated by the sympathetic nervous system and cause dilatation of the pupil thereby increasing the amount of light that can enter the eye I've highlighted the iris in green and slic the eyeball in half let's rotate around to view the eyeball in section and view the relationship of the iris to the other structures we have covered so far the inner layer of the eye consists of the retina the light detecting part of the eye the retina itself is comprised of two cellular layers the neural layer and the pigmented layer the neural layer consists of photo receptors the light detecting cells of the retina it is located posteriorly and laterally in the eye the pigmented layer lies underneath the neural layer and is attached to the chid lay it acts to support the neural lay and continues around the whole inner surface of the eye anteriorly the pigmented layer continues but the neural layer does not this part is known as the nonvisual retina posteriorly and laterally both layers of the retina are present this is the optic part of the retina the optic part of the retina can be viewed during opthalmoscope or fundoscopy the center of the retina is marked by an area known as the macula lutetia it is yellowish in color and highly pigmented the macula contains a depression called the fobia centralis which has a high concentration of cones which are the light sensitive receptor cells which function best in brightly lit conditions and are responsible for High accurity color vision the area that the optic nerve enters the retina is known as the optic disc it contains no light detecting cells and is therefore referred to as the blind spot of the retina the central retinal artery enters at this point and its branches are visible at this point when viewed during fundoscopy there are a few remaining structures to discuss to cover the basic gross anatomy of the eyeball there are two fluid areas in the eye known as the anterior and posterior Chambers the anterior chamber is located between the corer and the iris the posterior chamber is a small chamber located behind the iris and anterior to the lens and suspensory ligaments the two Chambers are continuous with one another via the pupillary opening the chambers filled with acreas humor which is a clear plasma likee fluid that nourishes and protects the eye the acous humor is secreted first into the posterior chamber and flows into the anterior chamber via the pupil and is then absorbed into the canal of schl also known as the scarl Venus sinus this channel encircles the eye lying at the point between the cornea and the iris you can see this highlighted in blue on this model if the drainage of acous humor is obstructed the intraocular pressure will rise a condition known as glaucoma the lens separates these two Chambers from the vitus chamber which fills the eyeball with a transparent gel-like substance known as vitous humor or Vitus body extending from behind the lens to the retina posteriorly so that's an overview of the gross anatomy of the eyeball in the next tutorial we'll take a look at the vascular Supply if you have enjoyed this video please click the like button below and subscribe for more video tutorials thank you for watching the 3D models used in this tutorial were powered by the excellent and free Anatomy learning app check it out for yourself